Technical Field
The present subject matter relates to circuitry for radio transmission, and more specifically, to a new design for a class-D amplifier and modulator.
Description of Related Art
FIG. 1 depicts a simplified circuit design of a conventional Class D amplifier. In a Class D amplifier, sometimes called a switching amplifier, the amplifying components—e.g., MOSFET transistors—operate as electronic switches rather than as linear gain devices, a typical use of MOSFETs. Conventional Class D amplifiers modulate the final power stage using a binary signal, typically pulse width modulation. This power stage transistor operates in an efficient manner because it is either fully on (saturated) or off (cutoff). As such, Class D amplifiers have been able to enjoy fairly good efficiencies.
However, because the transistor is operating fully saturated or cutoff, the frequency of operation of such a system is limited by the transistor switching speed. Class D amplification for audio frequencies (20 Hz to 20 kHz) are now ubiquitous. However, conventional Class D amplification for Radio Frequencies have been limited in the past to AM band (500 to 1700 kHz). Broadcast Electronics' 4MX AM Transmitter is an embodiment of a Class D amplifier in the AM band, as described in U.S. Pat. No. 7,092,269.